Apparatus for providing waveguide displays with two-dimensional pupil expansion

ABSTRACT

An optical display comprises: a first waveguide comprising a first surface and a second surface, an input coupler, a fold grating, and an output grating. The input coupler receives collimated first wavelength light from an Input Image Node causes the light to travel within the first waveguide via total internal reflection between the first surface and the second surface to the fold grating. The fold grating provides pupil expansion in a first direction directs the light to the output grating via total internal reflection between the first surface and the second surface. The output grating provides pupil expansion in a second direction different than the first direction and causes the light to exit the first waveguide from the first surface or the second surface. At least one of the input coupler, fold grating and output grating is a rolled k-vector grating, and the fold grating is a dual interaction grating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/118,285 entitled Apparatus for Providing Waveguide Displays withTwo-Dimensional Pupil Expansion filed on Dec. 10, 2020, whichapplication is a continuation of U.S. patent application Ser. No.16/806,947 entitled APPARATUS FOR PROVIDING WAVEGUIDE DISPLAYS WITHTWO-DIMENSIONAL PUPIL EXPANSION filed on Mar. 2, 2020, which applicationis a continuation of U.S. patent application Ser. No. 15/765,243entitled APPARATUS FOR PROVIDING WAVEGUIDE DISPLAYS WITH TWO-DIMENSIONALPUPIL EXPANSION filed on Mar. 30, 2018, which application is a nationalstage of PCT Application No. PCT/GB2016/00018 entitled WAVEGUIDE DISPLAYfiled on Oct. 4, 2016, which application claims priority to U.S.Provisional Patent Application No. 62/284,603 entitled WAVEGUIDE DISPLAYfiled on Oct. 5, 2015 and U.S. Provisional Patent Application No.62/285,275 entitled WAVEGUIDE DISPLAYS filed on Oct. 23, 2015, thedisclosures of which are incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

The present disclosure relates to displays including but not limited tonear eye displays and more particularly to holographic waveguidedisplays.

Waveguide optics is currently being considered for a range of displayand sensor applications for which the ability of waveguides to integratemultiple optical functions into a thin, transparent, lightweightsubstrate is of key importance. This new approach is stimulating newproduct developments including near-eye displays for Augmented Reality(AR) and Virtual Reality (VR), compact Heads Up Display (HUDs) foraviation and road transport and sensors for biometric and laser radar(LIDAR) applications. Waveguide displays have been proposed which usediffraction gratings to preserve eye box size while reducing lens size.U.S. Pat. No. 4,309,070 issued to St. Leger Searle and U.S. Pat. No.4,711,512 issued to Upatnieks disclose substrate waveguide head updisplays where the pupil of a collimating optical system is effectivelyexpanded by the waveguide structure. U.S. patent application Ser. No.13/869,866 discloses holographic wide angle displays and U.S. patentapplication Ser. No. 13/844,456 discloses waveguide displays having anupper and lower field of view.

A common requirement in waveguide optics is to provide beam expansion intwo orthogonal directions. In display applications this translates to alarge eyebox. While the principles of beam expansion in holographicwaveguides are well established dual axis expansion requires separategrating layers to provide separate vertical and horizontal expansion.One of the gratings, usually the one giving the second axis expansion,also provides the near eye component of the display where the hightransparency and thin, lightweight form factor of a diffractive opticscan be used to maximum effect. In practical display applications, whichdemand full color and large fields of view the number of layers requiredto implement dual axis expansion becomes unacceptably large resulting inincreased thickness weight and haze. Solutions for reducing the numberof layers based on multiplexing two or more gratings in a single layeror fold gratings which can perform dual axis expansion (for a givenangular range and wavelength) in a single layer are currently indevelopment. Dual axis expansion is also an issue in waveguides forsensor applications such as eye trackers and LIDAR. There is arequirement for a low cost, efficient, compact dual axis expansionwaveguide.

SUMMARY OF THE INVENTION

It is a first object of the invention to provide a low cost, efficient,compact dual axis expansion waveguide.

The object of the invention is achieved in first embodiment of theinvention in which there is provided an optical display, comprising: afirst waveguide comprising a first surface and a second surface, aninput coupler, a fold grating, and an output grating. The input coupleris configured to receive collimated first wavelength light from an InputImage Node (IIN) and to cause the light to travel within the firstwaveguide via total internal reflection between the first surface andthe second surface to the fold grating. The fold grating is configuredto provide pupil expansion in a first direction and to direct the lightto the output grating via total internal reflection between the firstsurface and the second surface. The output grating is configured toprovide pupil expansion in a second direction different than the firstdirection and to cause the light to exit the first waveguide from thefirst surface or the second surface. At least one of the input coupler,the fold grating or the output grating is a rolled k-vector grating. Thelight undergoes a dual interaction with the fold grating.

In some embodiments the IIN comprises a light source, a microdisplay fordisplaying image pixels and collimation optics. The IIN projects theimage displayed on the microdisplay panel such that each image pixel isconverted into a unique angular direction within the first waveguide

In some embodiments at least one of the gratings is switchable between adiffracting and non-diffracting state.

In some embodiments the optical display further comprises a secondwaveguide comprising a first surface and a second surface, an inputcoupler, a fold grating, and an output grating, wherein the inputcoupler is configured to receive collimated second wavelength light fromthe IIN.

In some embodiments at least one of the input coupler, the fold grating,and the output grating is a liquid crystal-based grating.

In some embodiments the first direction is orthogonal to the seconddirection.

In some embodiments the first direction is horizontal and the seconddirection is vertical.

In some embodiments the optical display further comprises an eyetracker.

In some embodiments the optical display further comprises a dynamicfocus lens disposed in the IIN.

In some embodiments the optical display further comprises a dynamicfocus lens disposed in proximity to the first or second surface of thefirst waveguide.

In some embodiments the first waveguide further comprises a firstoptical interface the IIN further comprises a second optical interfacewherein the first and second optical interface can be decoupled by oneof a mechanical mechanism or a magnetic mechanism.

In some embodiments the first waveguide is disposable. In someembodiments the first surface and the second surface are planarsurfaces. In some embodiments the first surface and the second surfaceare curved surfaces. In some embodiments the IIN comprises a laserscanner.

In some embodiments the display provides one of a HMD, a HUD, aneye-slaved display, a dynamic focus display or a light field display.

In some embodiments at least one of the input coupler, fold grating andoutput grating multiplexes at least one of color or angle.

In some embodiments the optical display further comprises a beamhomogenizer.

In some embodiments the display includes at least one optical traversinga gradient index image transfer waveguide.

In some embodiments the optical display further comprises a dichroicfilter disposed between the input grating regions of the first andsecond waveguides.

In some embodiments the IIN further comprises a spatially-varyingnumerical aperture component for providing a numerical aperturevariation along a direction corresponding to the field of viewcoordinate diffracted by the input coupler.

In some embodiments the spatially-varying numerical aperture componenthas at least one of diffractive, birefringent, refracting or scatteringcharacteristics.

In some embodiments the field of view coordinate is the horizontal fieldof view of the display.

In some embodiments a spatially varying-numerical aperture is providedby tilting a stop plane such that its normal vector is alignedperpendicular to the highest display field angle in the plane containingthe field of view coordinate diffracted by the input coupler.

One exemplary embodiment of the disclosure relates to a near eye opticaldisplay. The near eye optical display includes a waveguide comprising afirst surface and a second surface, an input coupler, a fold grating,and an output grating. The input coupler is configured to receivecollimated light from a display source and to cause the light to travelwithin the waveguide via total internal reflection between the firstsurface and the second surface to the fold grating. The fold grating isconfigured to provide pupil expansion in a first direction and to directthe light to the output grating via total internal reflection betweenthe first surface and the second surface. The output grating isconfigured to provide pupil expansion in a second direction differentthan the first direction and to cause the light to exit the waveguidefrom the first surface or the second surface.

Another exemplary embodiment of the disclosure relates to a method ofdisplaying information. The method includes receiving collimated lightin a waveguide having a first surface and a second surface; providingthe collimated light to a fold grating via total internal reflectionbetween the first surface and the second surface; providing pupilexpansion in a first direction using the fold grating and directing thelight to an output grating via total internal reflection between thefirst surface and the second surface; and providing pupil expansion in asecond direction different than the first direction and causing thelight to exit the waveguide from the first surface or the secondsurface.

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, an inventive optical display and methodsfor displaying information. It should be appreciated that variousconcepts introduced above and discussed in greater detail below may beimplemented in any of numerous ways, as the disclosed concepts are notlimited to any particular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes. A more complete understanding of the invention can be obtainedby considering the following detailed description in conjunction withthe accompanying drawings, wherein like index numerals indicate likeparts. For purposes of clarity, details relating to technical materialthat is known in the technical fields related to the invention have notbeen described in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section view of a waveguide display in oneembodiment.

FIG. 2 is a schematic plan view of a waveguide display shown thedisposition of the gratings in one grating layer in one embodiment.

FIG. 3 is a schematic plan view of a waveguide display shown thedisposition of the gratings in two grating layers in one embodiment.

FIG. 4 is a schematic cross section view of a color waveguide displayusing one waveguide per color and two grating layers in each waveguidein one embodiment.

FIG. 5 is a schematic cross section view of a color waveguide displayusing one waveguide per color and one grating layer in each waveguide inone embodiment.

FIG. 6 is a schematic plan view of a waveguide display showing an inputgrating a fold grating and an output grating in one embodiment.

FIG. 7 is a cross section view of an eye tracked near eye displayaccording to the principles of the invention in one embodiment.

FIG. 8 is a cross section view of an eye tracked near eye displayincorporating a dynamic focus lens in one embodiment.

FIG. 9 is a cross section view of an eye tracked near eye displayincorporating a dynamic focus lens in one embodiment.

FIG. 10A is a schematic plan view of a first operational state displaycomprising a waveguide that can be decoupled from the IIN in oneembodiment.

FIG. 10B is a schematic plan view of a second operational state displaycomprising a waveguide that can be decoupled from the IIN in oneembodiment.

FIG. 11A is a rolled K-vector grating providing stepwise changes inK-vector direction in one embodiment.

FIG. 11B is a rolled K-vector grating providing continuous changes inK-vector direction in one embodiment.

FIG. 12A is front view of a waveguide display eyepiece in oneembodiment.

FIG. 12B is plan view of a waveguide display eyepiece in one embodiment.

FIG. 12C is side view of a waveguide display eyepiece in one embodiment.

FIG. 12D is a three dimensional view of a waveguide display eyepiece inone embodiment.

FIG. 13A is a three dimensional view of a waveguide display implementedin a motorcycle helmet in one embodiment.

FIG. 13B is another three dimensional view of a waveguide displayimplemented in a motorcycle helmet in one embodiment.

FIG. 14 is a schematic cross section view of a reflective microdisplayinput image node containing a spatially-varying numerical aperturecomponent in one embodiment.

FIG. 15 is a schematic cross section view of a reflective microdisplayinput image node containing a spatially-varying numerical aperturecomponent in one embodiment.

FIG. 16 is a schematic cross section view of a transmissive microdisplayinput image node containing a spatially-varying numerical aperturecomponent in one embodiment.

FIG. 17 is a schematic cross section view of an emissive microdisplayinput image node containing a spatially-varying numerical aperturecomponent in one embodiment.

FIG. 18A is a schematic cross section view of a spatially-varyingnumerical aperture component based on a wedge prism in one embodiment.

FIG. 18B is a schematic cross section view of a spatially-varyingnumerical aperture component based on a wedge prism with one curvedsurface in one embodiment.

FIG. 18C is a schematic cross section view of a spatially-varyingnumerical aperture component based on an array of prisms in oneembodiment.

FIG. 18D is a schematic cross section view of a spatially-varyingnumerical aperture component based on an array of lenses in oneembodiment.

FIG. 19A is a schematic cross section view of a spatially-varyingnumerical aperture component based on an array of scattering elements inone embodiment.

FIG. 19B is a schematic cross section view of a spatially-varyingnumerical aperture component based on a substrate with a continuouslyvarying scattering function in one embodiment.

FIG. 19C is a schematic cross section view of a spatially-varyingnumerical aperture component based on a substrate with a continuouslyvarying birefringence tensor in one embodiment.

FIG. 19D is a schematic cross section view of a spatially-varyingnumerical aperture component based on an array of grating elements inone embodiment.

FIG. 20 is a schematic cross section view of an optical arrangement forproviding varying numerical aperture across a pupil using a tilted pupilplane in one embodiment.

FIG. 21A is a three dimensional view of a first operational state of awearable display comprising a retractable waveguide in one embodiment.

FIG. 21B is a three dimensional view of a second operational state of awearable display comprising a retractable waveguide in one embodiment.

FIG. 21C is a three dimensional view of a third operational state of awearable display comprising a retractable waveguide in one embodiment.

FIG. 22A is front view of a waveguide component showing the input, foldand output gratings in one embodiment.

FIG. 22B is front view of a waveguide component showing the input, foldand output gratings in one embodiment.

FIG. 23 is front view of a waveguide component showing the input, foldand output gratings in one embodiment.

FIG. 24 is a three dimensional view of a near eye display showing a raytrace from the IIN and waveguide component up to the eye box in oneembodiment.

FIG. 25A is a three dimensional view of a first operational state of amotorcycle display in one embodiment.

FIG. 25B is a three dimensional view of a second operational state of amotorcycle display in one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be further described by way of example only withreference to the accompanying drawings. It will apparent to thoseskilled in the art that the present invention may be practiced with someor all of the present invention as disclosed in the followingdescription. For the purposes of explaining the invention well-knownfeatures of optical technology known to those skilled in the art ofoptical design and visual displays have been omitted or simplified inorder not to obscure the basic principles of the invention. Unlessotherwise stated the term “on-axis” in relation to a ray or a beamdirection refers to propagation parallel to an axis normal to thesurfaces of the optical components described in relation to theinvention. In the following description the terms light, ray, beam anddirection may be used interchangeably and in association with each otherto indicate the direction of propagation of electromagnetic radiationalong rectilinear trajectories. The term light and illumination may beused in relation to the visible and infrared bands of theelectromagnetic spectrum. Parts of the following description will bepresented using terminology commonly employed by those skilled in theart of optical design. It should also be noted that in the followingdescription of the invention repeated usage of the phrase “in oneembodiment” does not necessarily refer to the same embodiment.

Referring generally to the Figures, systems and methods relating tonear-eye display or head up display systems are shown according tovarious embodiments. Holographic waveguide technology can beadvantageously utilized in waveguides for helmet mounted displays orhead mounted displays (HMDs) and head up displays (HUDs) for manyapplications, including military applications and consumer applications(e.g., augmented reality glasses, etc.). Switchable Bragg gratings(SBGs) may be used in waveguides to eliminate extra layers and to reducethe thickness of current display systems, including HMDs, HUDs, andother near eye displays and to increase the field of view by tilingimages presented sequentially on a microdisplay. A larger exit pupil maybe created by using fold gratings in conjunction with conventionalgratings to provide pupil expansion on a single waveguide in both thehorizontal and vertical directions. Using the systems and methodsdisclosed herein, a single optical waveguide substrate may generate awider field of view than found in current waveguide systems. Diffractiongratings may be used to split and diffract light rays into several beamsthat travel in different directions, thereby dispersing the light rays.

The grating used in the invention is desirably a Bragg grating (alsoreferred to as a volume grating). Bragg gratings have high efficiencywith little light being diffracted into higher orders. The relativeamount of light in the diffracted and zero order can be varied bycontrolling their refractive index modulation of the grating, a propertywhich is used to make lossy waveguide gratings for extracting light overa large pupil. One important class of gratings is known as SwitchableBragg Gratings (SBG). SBGs are fabricated by first placing a thin filmof a mixture of photopolymerizable monomers and liquid crystal materialbetween parallel glass plates. One or both glass plates supportelectrodes, typically transparent indium tin oxide films, for applyingan electric field across the film. A volume phase grating is thenrecorded by illuminating the liquid material (often referred to as thesyrup) with two mutually coherent laser beams, which interfere to form aslanted fringe grating structure. During the recording process, themonomers polymerize and the mixture undergoes a phase separation,creating regions densely populated by liquid crystal micro-droplets,interspersed with regions of clear polymer. The alternating liquidcrystal-rich and liquid crystal-depleted regions form the fringe planesof the grating. The resulting volume phase grating can exhibit very highdiffraction efficiency, which may be controlled by the magnitude of theelectric field applied across the film. When an electric field isapplied to the grating via transparent electrodes, the naturalorientation of the LC droplets is changed causing the refractive indexmodulation of the fringes to reduce and the hologram diffractionefficiency to drop to very low levels. Typically, SBG Elements areswitched clear in 30 μs. With a longer relaxation time to switch ON.Note that the diffraction efficiency of the device can be adjusted, bymeans of the applied voltage, over a continuous range. The deviceexhibits near 100% efficiency with no voltage applied and essentiallyzero efficiency with a sufficiently high voltage applied. In certaintypes of HPDLC devices magnetic fields may be used to control the LCorientation. In certain types of HPDLC phase separation of the LCmaterial from the polymer may be accomplished to such a degree that nodiscernible droplet structure results. A SBG may also be used as apassive grating. In this mode its chief benefit is a uniquely highrefractive index modulation.

SBGs may be used to provide transmission or reflection gratings for freespace applications. SBGs may be implemented as waveguide devices inwhich the HPDLC forms either the waveguide core or an evanescentlycoupled layer in proximity to the waveguide. The parallel glass platesused to form the HPDLC cell provide a total internal reflection (TIR)light guiding structure. Light is coupled out of the SBG when theswitchable grating diffracts the light at an angle beyond the TIRcondition. Waveguides are currently of interest in a range of displayand sensor applications. Although much of the earlier work on HPDLC hasbeen directed at reflection holograms transmission devices are provingto be much more versatile as optical system building blocks. Typically,the HPDLC used in SBGs comprise liquid crystal (LC), monomers,photoinitiator dyes, and coinitiators. The mixture frequently includes asurfactant. The patent and scientific literature contains many examplesof material systems and processes that may be used to fabricate SBGs.Two fundamental patents are: U.S. Pat. No. 5,942,157 by Sutherland, andU.S. Pat. No. 5,751,452 by Tanaka et al. Both filings describe monomerand liquid crystal material combinations suitable for fabricating SBGdevices. One of the known attributes of transmission SBGs is that the LCmolecules tend to align normal to the grating fringe planes. The effectof the LC molecule alignment is that transmission SBGs efficientlydiffract P polarized light (i.e. light with the polarization vector inthe plane of incidence) but have nearly zero diffraction efficiency forS polarized light (i.e. light with the polarization vector normal to theplane of incidence. Transmission SBGs may not be used at near-grazingincidence as the diffraction efficiency of any grating for Ppolarization falls to zero when the included angle between the incidentand reflected light is small.

The object of the invention is achieved in first embodiment illustratedin FIG. 1 in which there is provided a dual axis expansion waveguidedisplay 100 comprising a light source 101 a microdisplay panel 102 andan input image node (IIN) 103 optically coupled to a waveguide 104comprise two grating layers 104A,104B. In some embodiments the waveguideis formed by sandwiched the grating layers between glass or plasticsubstrates to form a stack within which total internal reflection occursat the outer substrate and air interfaces. The stack may furthercomprise additional layers such as beam splitting coatings andenvironmental protection layers. Each grating layer contains an inputgrating 105A,105B, a fold grating exit pupil expander 106A,106B and anoutput grating 107A,107B where characters A and B refer to waveguidelayers 104A,104B respectively. The input grating, fold grating and theoutput grating are holographic gratings, such as a switchable ornon-switchable SBG. As used herein, the term grating may encompass agrating comprised of a set of gratings in some embodiments. In generalthe IIN integrates a microdisplay panel, light source and opticalcomponents needed to illuminate the display panel, separate thereflected light and collimate it into the required FOV. In theembodiment of FIG. 1 and in the embodiments to be described below atleast one of the input fold and output gratings may be electricallyswitchable. In many embodiments it is desirable that all three gratingtypes are passive, that is, non-switching. The IIN projects the imagedisplayed on the microdisplay panel such that each display pixel isconverted into a unique angular direction within the substrate waveguideaccording to some embodiments. The collimation optics contained in theIIN may comprise lens and mirrors which is some embodiments may bediffractive lenses and mirrors.

In some embodiments the IIN may be based on the embodiments andteachings disclosed in U.S. patent application Ser. No. 13/869,866entitled HOLOGRAPHIC WIDE ANGLE DISPLAY, and U.S. patent applicationSer. No. 13/844,456 entitled TRANSPARENT WAVEGUIDE DISPLAY. In someembodiments the IIN contains beamsplitter for directing light onto themicrodisplay and transmitting the reflected light towards the waveguide.In one embodiment the beamsplitter is a grating recorded in HPDLC anduses the intrinsic polarization selectivity of such gratings to separatethe light illuminating the display and the image modulated lightreflected off the display. In some embodiments the beam splitter is apolarizing beam splitter cube. In some embodiment the IIN incorporates adespeckler. Advantageously, the despeckler is holographic waveguidedevice based on the embodiments and teachings of U.S. Pat. No. 8,565,560entitled LASER ILLUMINATION DEVICE.

The light source can be a laser or LED and can include one or morelenses for modifying the illumination beam angular characteristics. Theimage source can be a micro-display or laser based display. LED willprovide better uniformity than laser. If laser illumination is usedthere is a risk of illumination banding occurring at the waveguideoutput. In some embodiments laser illumination banding in waveguides canbe overcome using the techniques and teachings disclosed in U.S.Provisional Patent Application No. 62/071,277 entitled METHOD ANDAPPARATUS FOR GENERATING INPUT IMAGES FOR HOLOGRAPHIC WAVEGUIDEDISPLAYS. In some embodiments, the light from the light source 101 ispolarized. In one or more embodiments, the image source is a liquidcrystal display (LCD) micro display or liquid crystal on silicon (LCoS)micro display.

The light path from the source to the waveguide via the IIN is indicatedby rays 1000-1003. The input grating of each grating layer couples aportion of the light into a TIR path in the waveguide once such pathbeing represented by the rays 1004-1005. The output waveguides 107A,107Cdiffract light out of the waveguide into angular ranges of collimatedlight 1006,1007 respectively for viewing by the eye 108. The angularranges, which correspond to the field of view of the display, aredefined solely by the IIN optics. In some embodiments the waveguidegratings may encoded optical power for adjusting the collimation of theoutput. In some embodiments the output image is at infinity. In someembodiments the output image may be formed at distances of severalmeters from the eye box. Typically the eye is positioned within the exitpupil or eye box of the display.

In some embodiments similar to the one shown in FIG. 1 each gratinglayer addresses half the total field of view. Typically, the foldgratings are clocked (that is, tilted in the waveguide plane) at 45° toensure adequate angular bandwidth for the folded light. However someembodiments of the invention may use other clock angles to satisfyspatial constraints on the positioning of the gratings that may arise inthe ergonomic design of the display. In some embodiments at least one ofthe input and output gratings have rolled k-vectors. The K-vector is avector aligned normal to the grating planes (or fringes) whichdetermines the optical efficiency for a given range of input anddiffracted angles. Rolling the K-vectors allows the angular bandwidth ofthe grating to be expanded without the need to increase the waveguidethickness.

In some embodiments the fold grating angular bandwidth can be enhancedby designing the grating prescription provides dual interaction of theguided light with the grating. Exemplary embodiments of dual interactionfold gratings are disclosed in U.S. patent application Ser. No.14/620,969 entitled WAVEGUIDE GRATING DEVICE.

It is well established in the literature of holography that more thanone holographic prescription can be recorded into a single holographiclayer. Methods for recording such multiplexed holograms are well knownto those skilled in the art. In some embodiments at least one of theinput, fold or output gratings may combine two or more angulardiffraction prescriptions to expand the angular bandwidth. Similarly, insome embodiments at least one of the input, fold or output gratings maycombine two or more spectral diffraction prescriptions to expand thespectral bandwidth. For example a color multiplexed grating may be usedto diffract two or more of the primary colors.

FIG. 2 is a plan view 110 of a single grating layer similar to the onesused in FIG. 1 . The grating layer 111 which is optically coupled to theIIN 112 comprising input grating 113, a first beamsplitter 114, a foldgrating 115, a second beamsplitter 116 and an output grating 117. Thebeamsplitter are partially transmitting coatings which homogenise thewave guided light by providing multiple reflection paths within thewaveguide. Each beamsplitter may comprise more than one coating layerwith each coating layer being applied to a transparent substrates.Typical beam paths from the IIN up to the eye 118 are indicated by therays 1010-1014.

FIG. 3 is a plan view 110 of a two grating layer configuration similarto the ones used in FIG. 1 The grating layers 121A,121B which areoptically coupled to the IIN 122 comprise input gratings 123A,123B,first beamsplitters 124A,124B, fold gratings 125A,125B, secondbeamsplitters 126A,126B and output gratings 127A,127B, where thecharacters A, B refer to the first and second grating layers and thegratings and beams splitters of the two layers substantially overlap.

In the most waveguide configurations the input fold and output gratingsare formed in a single layer sandwiched by transparent substrates. Theembodiment of FIG. 1 has two such layers stacked. In some embodimentsthe waveguide may comprise just one grating layer. The substrates arenot illustrated in FIG. 1 where the gratings are switching transparentelectrodes are applied to opposing surfaces of the substrate layerssandwiching the switching grating. In some embodiments the cellsubstrates may be fabricated from glass. An exemplary glass substrate isstandard Corning Willow glass substrate (index 1.51) which is availablein thicknesses down to 50 micron. In other embodiments the cellsubstrates may be optical plastics.

In some embodiments the grating layer may be broken up into separatelayers. For example, in some embodiments, a first layer includes thefold grating while a second layer includes the output grating. In someembodiments, a third layer can include the input grating. The number oflayers may then be laminated together into a single waveguide substrate.In some embodiments, the grating layer is comprised of a number ofpieces including the input coupler, the fold grating and the outputgrating (or portions thereof) that are laminated together to form asingle substrate waveguide. The pieces may be separated by optical glueor other transparent material of refractive index matching that of thepieces. In another embodiment, the grating layer may be formed via acell making process by creating cells of the desired grating thicknessand vacuum filling each cell with SBG material for each of the inputcoupler, the fold grating and the output grating. In one embodiment, thecell is formed by positioning multiple plates of glass with gaps betweenthe plates of glass that define the desired grating thickness for theinput coupler, the fold grating and the output grating. In oneembodiment, one cell may be made with multiple apertures such that theseparate apertures are filled with different pockets of SBG material.Any intervening spaces may then be separated by a separating material(e.g., glue, oil, etc.) to define separate areas. In one embodiment theSBG material may be spin-coated onto a substrate and then covered by asecond substrate after curing of the material. By using the foldgrating, the waveguide display advantageously requires fewer layers thanprevious systems and methods of displaying information according to someembodiments. In addition, by using fold grating, light can travel bytotal internal refection within the waveguide in a single rectangularprism defined by the waveguide outer surfaces while achieving dual pupilexpansion. In another embodiment, the input coupler, the fold gratingand the output grating can be created by interfering two waves of lightat an angle within the substrate to create a holographic wave front,thereby creating light and dark fringes that are set in the waveguidesubstrate 101 at a desired angle. In some embodiments the grating in agiven layer is recorded in stepwise fashion by scanning or stepping therecording laser beams across the grating area. N some embodiments thegratings are recorded using mastering and contact copying processcurrently used in the holographic printing industry.

In one embodiment, the input coupler, the fold grating, and the outputgrating embodied as SBGs can be Bragg gratings recorded in a holographicpolymer dispersed liquid crystal (HPDLC) (e.g., a matrix of liquidcrystal droplets), although SBGs may also be recorded in othermaterials. In one embodiment, SBGs are recorded in a uniform modulationmaterial, such as POLICRYPS or POLIPHEM having a matrix of solid liquidcrystals dispersed in a liquid polymer. The SBGs can be switching ornon-switching in nature. In its non switching form an SBG has theadvantage over conventional holographic photopolymer materials of beingcapable of providing high refractive index modulation due to its liquidcrystal component. Exemplary uniform modulation liquid crystal-polymermaterial systems are disclosed in United State Patent ApplicationPublication No.: US2007/0019152 by Caputo et al and PCT Application No.:PCT/EP2005/006950 by Stumpe et al. both of which are incorporated hereinby reference in their entireties. Uniform modulation gratings arecharacterized by high refractive index modulation (and hence highdiffraction efficiency) and low scatter.

In one embodiment, the input coupler, the fold grating, and the outputgrating a reverse mode HPDLC material. Reverse mode HPDLC differs fromconventional HPDLC in that the grating is passive when no electric fieldis applied and becomes diffractive in the presence of an electric field.The reverse mode HPDLC may be based on any of the recipes and processesdisclosed in PCT Application No.: PCT/GB2012/000680, entitledIMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALSAND DEVICES. The grating may be recorded in any of the above materialsystems but used in a passive (non-switching) mode. The fabricationprocess is identical to that used for switched but with the electrodecoating stage being omitted. LC polymer material systems are highlydesirable in view of their high index modulation. In some embodimentsthe gratings are recorded in HPDLC but are not switched.

In some embodiments the input grating may be replaced by another type ofinput coupler such as a prism, or reflective surface. In someembodiments, the input coupler can be a holographic grating, such as aswitchable or non-switchable SBG grating. The input coupler isconfigured to receive collimated light from a display source and tocause the light to travel within the waveguide via total internalreflection between the first surface and the second surface to the foldgrating. The input coupler may be orientated directly towards or at anangle relative to the fold grating. For example, in one embodiment, theinput coupler may be set at a slight incline in relation to the foldgrating.

In some embodiments, the fold grating may be oriented in a diagonaldirection. The fold grating is configured to provide pupil expansion ina first direction and to direct the light to the output grating viatotal internal reflection inside the waveguide in some embodiments.

In one embodiment, a longitudinal edge of each fold grating is obliqueto the axis of alignment of the input coupler such that each foldgrating is set on a diagonal with respect to the direction ofpropagation of the display light. The fold grating is angled such thatlight from the input coupler is redirected to the output grating. In oneexample, the fold grating is set at a forty-five degree angle relativeto the direction that the display image is released from the inputcoupler. This feature causes the display image propagating down the foldgrating to be turned into the output grating. For example, in oneembodiment, the fold grating causes the image to be turned 90 degreesinto the output grating. In this manner, a single waveguide providesdual axis pupil expansion in both the horizontal and verticaldirections. In one embodiment, each of the fold grating may have apartially diffractive structure.

In some embodiments, each of the fold gratings may have a fullydiffractive structure. In some embodiments, different gratingconfigurations and technologies may be incorporated in a singlewaveguide.

The output grating is configured to provide pupil expansion in a seconddirection different than the first direction and to cause the light toexit the waveguide from the first surface or the second surface. Theoutput grating receives the display image from the fold grating viatotal internal reflection and provides pupil expansion in a seconddirection. In some embodiments, the output grating consists of multiplelayers of substrate, thereby comprising multiple layers of outputgratings. Accordingly, there is no requirement for gratings to be in oneplane within the waveguide, and gratings may be stacked on top of eachother (e.g., cells of gratings stacked on top of each other).

In some embodiments, a quarter wave plate on the substrate waveguiderotates polarization of a light ray to maintain efficient coupling withthe SBGs. The quarter wave plate may be coupled to or adhered to thesurface of substrate waveguide 101. For example, in one embodiment, thequarter wave plate is a coating that is applied to substrate waveguide.The quarter wave plate provides light wave polarization management. Suchpolarization management may help light rays retain alignment with theintended viewing axis by compensating for skew waves in the waveguide.The quarter wave plate is optional and can increase the efficiency ofthe optical design in some embodiments. In some embodiments, thewaveguide does not include the quarter wave plate 142. The quarter waveplate may be provided as multi-layer coating.

The embodiment of FIG. 1 would normally be operated in monochrome. Acolor would comprises a stack of monochrome waveguides of similar designto the one in FIG. 1 . The design may use red green and blue waveguidelayers as shown or, alternatively, red and blue/green layers. In theembodiment of FIG. 5 the dual axis expansion waveguide display 130comprises a light source 132 a microdisplay panel 131 and an input imagenode (IIN) 133 optically coupled to red, green and blue waveguides134R,134G,134B each comprise two grating layers. In order that waveguiding can take place in each waveguide the three waveguides areseparated by air gaps. In some embodiments the waveguides are separatedby a low index material such as a nanoporous film. The red grating layerlabelled by R contains an input grating 135R,136R, a fold grating exitpupil expander 137R,138R and an output grating 139R,140R. The gratingelements of the blue and green waveguides are labeled using the samenumerals with B, G designating blue and red. Since the light pathsthrough the IIN and waveguides in each of the red green and bluewaveguides are similar to those illustrated in FIG. 1 they are notsshown in FIG. 4 . In some embodiments the input, fold and outputgratings are all passive, that is non-switching. In some embodiments atleast one of the gratings is switching. In some embodiments the inputgratings in each layer are switchable to avoid color crosstalk betweenthe waveguide layers. In some embodiments color crosstalk is avoided bydisposing dichroic filters 141,142 between the input grating regions ofthe red and blue and the blue and green waveguides.

In some embodiments a color waveguide based may use just one gratinglayer in each monochromatic waveguide. In the embodiment shown in FIG. 5, which is similar to the one of FIG. 4 , the dual axis expansionwaveguide display 150 comprises a light source 132, a microdisplay panel131 and an input image node (IIN) 133 optically coupled to red, greenand blue waveguides 151R,151G,151B each comprising one grating layer.The red grating layer labelled by R contains an input grating 152R, afold grating exit pupil expander 153R and an output grating 154R. Thegrating elements of the blue and green waveguides are labeled using thesame numerals with B, G designating blue and red. Dichroic filters155,156 are disposed between the input grating regions of the red andblue and the blue and green waveguides to control color crosstalk. Sincethe light paths through the IIN and waveguides in each of the red greenand blue waveguides are similar to those illustrated in FIG. 1 they arenots shown in FIG. 5 .

FIG. 6 is a plan view of a grating layer 160 in a waveguide displayshowing a layout comprising an input grating 163, a fold grating 162 andan output grating 163. Gratings are shaded using lines showing theorientations the grating fringes with the input grating fringes beingaligned at 90 degrees to the X coordinate of the Cartesian referenceframe shown, the fold grating fringes at 45 degrees and the outputgrating fringes at 0 degrees.

In one embodiment of the invention shown in FIG. 7 there is provided aneye tracked display comprising a waveguide display according to theprinciples of the invention and an eye tracker. In one preferredembodiment the eye tracker is a waveguide device based on theembodiments and teachings of PCT/GB2014/000197 entitled HOLOGRAPHICWAVEGUIDE EYE TRACKER, PCT/GB2015/000274 entitled HOLOGRAPHIC WAVEGUIDEOPTICALTRACKER, and PCT Application No.: GB2013/000210 entitledAPPARATUS FOR EYE TRACKING. Turning again to FIG. 7 the eye trackeddisplay 170 comprises a dual axis expansion waveguide display based onany of the above embodiments comprising the waveguide 171 containing atleast one grating layer incorporating an input fold and output grating,the IIN 173, the eye tracker comprising the waveguide 173, infrareddetector 174 and infrared source 175. The eye tracker and displaywaveguides are separate by an air gap or by a low refractive material.As is explained in the above references, the eye tracker may compriseseparate illumination and detector waveguides. The optical path from theinfrared source to the eye is indicated by the rays 1033-1035 and thebackscattered signal from the eye is indicated by the rays 1036-1037.The display comprises a waveguide 966 and an input image node 968. Theoptical path from the input image node through the display waveguide tothe eye box is indicated by the rays 1030-1032.

In some embodiments of the invention a dual expansion waveguide displayfurther comprises a dynamic focusing element. In some embodiments suchas the one shown in FIG. 8 a dual expansion waveguide display 180further comprises a dynamic focusing element 181 disposed in proximityto a principal surface of the waveguide display and an eye tracker.Advantageously the dynamic focusing element is a LC device. In someembodiments the LC device combines an LC layer and a diffractive opticalelement. In some embodiments the diffractive optical element is anelectrically controllable LC-based device. In some embodiments thedynamic focusing element is disposed between the waveguide display andthe eye tracker. In some embodiments the dynamic focusing element may bedisposed in proximity to the surface of the display waveguide furthestfrom the eye. In some embodiments such as the one illustrated in FIG. 9the dual expansion waveguide display 190 includes a dynamic focusingelement 191 disposed within the IIN The effect of the dynamic focusdevice is to provide a multiplicity of image surfaces 1040. In lightfield display applications at least four image surfaces are required.The dynamic focusing element may be based on the embodiments andteachings of U.S. Provisional Patent Application No. 62/176,572 entitledELECTRICALLY FOCUS TUNABLE LENS. In some embodiment a dual expansionwaveguide display further comprising a dynamic focusing element and aneye tracker may provide a light field display based on the embodimentsand teachings disclosed in U.S. Provisional Patent Application No.62/125,089 entitled HOLOGRAPHIC WAVEGUIDE LIGHT FIELD DISPLAYS.

In some embodiments the waveguide display is coupled to the IIN by anopto-mechanical interface that allows the waveguide to be easilyretracted from the IIN assembly. The basic principle is illustrated inFIG. 10A which shows a dual axis expansion waveguide display 200comprising the waveguide 201 containing the input grating 202, foldgrating 203 and output grating 204 and the IIN 205. The apparatusfurther comprises an optical link 206 connected to the waveguide, afirst optical interface 207 terminating the optical link and a secondoptical interface 208 forming the exit optical port of the IIN. Thefirst and second optical interfaces can be decoupled as indicated by thegap 209 shown in FIG. 10B. In some embodiments the optical link is awaveguide. In some embodiments the optical link is curved. In someembodiments the optical link is a GRIN image relay device. In someembodiments the optical connection is established using a mechanicalmechanism. In some embodiments the optical connection is establishedusing a magnetic mechanism. The advantage of decoupling the waveguidefrom the IIN in helmet mounted display applications is that the near eyeportion of the display be removed when not in used. In some embodimentswhere the waveguide comprises passive gratings the near eye optics canbe disposable.

FIG. 11 illustrates rolled K-vector gratings for use with the invention.Referring first to FIG. 11A, in some embodiments a rolled K-vectorgrating 220 is implemented as a waveguide portion containing thediscrete grating elements 212-215 having K-vectors 1050-1053. Referringnext to FIG. 11B, in some embodiments a rolled K-vector grating 220 isimplemented as a waveguide portion containing grating elements 222within which the K-vectors undergoes a smooth monotonic variation indirection including the illustrated directions 1050-1053.

FIGS. 12A-12D illustrated front, plan, side and three dimensions viewsof one eyepiece of a dual axis expansion display used in a motorcyclehelmet mount display in one embodiment. The display comprises thewaveguide 231, input grating 232, fold grating 233, output grating 234,a hinge mechanism 235 for attaching the display to the helmet and thewaveguide coupling mechanism 236. FIG. 13A-FIG. 13B show threedimensional views of the eyepiece integrated in a motorcycle helmet.

In practical embodiments of the invention care must be taken to ensurethat the IIN is optically matched to the waveguide. Waveguides raiseoptical interfacing issues that are not encountered in conventionaloptical systems in particular matching the input image angular contentto the angular capacity of the waveguide and input grating. The opticaldesign challenge is to match the IIN aperture variation as a function offield angle to the rolled K-vector input grating diffraction direction.Desirably the waveguide should be designed to make the waveguidethickness as small as possible while maximizing the spread of fieldangles at any given point on the input grating, subject to the limitsimposed by the angular bandwidth of the input grating, and the angularcarrying capacity of the waveguide. From consideration of the abovedescription and the teachings of earlier filings such it should beappreciated that coupling collimated angular image content over the fullfield of view and without significant non-uniformity of the illuminationdistribution across the pupil requires a numerical aperture (NA)variation ranging from high NA on one side of the microdisplay fallingsmoothly to a low NA at the other side. For the purposes of explainingthe invention the NA is defined as being proportional to the sine of themaximum angle of the image ray cone from a point on the microdisplaysurface with respect to an axis normal to the microdisplay. Otherequivalent measures may be used for the purposes of determining the mostoptimal IIN to waveguide coupling. Controlling the NA in this way willensure high optical efficiency and reduced banding and otherillumination non-homogeneities in the case of LED-illuminated displays.Laser-illuminated displays will also benefit from the control of NAvariation across the microdisplay particular with regard to homogeneity.

The following embodiments address the problem of varying the NA. In oneembodiment using angle selective coatings, gratings wedges, microelements, freeform elements, etc, inside the IIN. We shall refer to theXYZ Cartesian coordinate system shown in the drawings. For the purposesof explain the invention the Z axis is normal to the waveguide andeyebox planes. The Y and X axes are vertical and horizontalrespectively. The rolled-K vectors gratings have their K-vectors tiltedin the X-Z plane. Image light in the waveguide propagates substantiallyin the X-direction. In the following paragraphs we shall describeschemes for varying the NA from high to low (or vice versa) across thehorizontal axis of the microdisplay that is along the X-direction. Insome embodiments the microdisplay is an LCoS device.

In one embodiment shown in FIG. 14 the IIN 250 comprises a microdisplaypanel 251 a spatially-varying NA component 252 and microdisplay optics253. The microdisplay optics accepts light 1060 from an illuminationsource which is not illustrated and deflects the light on to themicrodisplay in the direction indicated by the ray 1061. The lightreflected from the microdisplay is indicated by the divergent ray pairs1062-1064 with NA angles varying along the X axis. In embodiments basedon FIG. 14 the spatially-varying NA component is disposed between themicrodisplay optics and the microdisplay. In some embodiments thespatially-varying NA component is disposed adjacent the output surfaceof the microdisplay optics as illustrated in FIG. 15 which shows amicrodisplay 261, illumination component 262, spatially-varying NAcomponent 263 with input illumination and illumination emitted from themicrodisplay optics onto the microdisplay as indicated by the rays1070,1071. The light reflected from the microdisplay is indicated by thedivergent ray pairs 1072-1074 with NA angles varying along the X axis.

In the embodiments of FIGS. 14-15 the microdisplay is a reflectivedevice. In some embodiments the microdisplay is a transmission device,typically a transmission LCoS device. In the embodiment of FIG. 16 theIIN 260 comprises the backlight 261, a microdisplay 262 and a variableNA component 263. Light from the backlight indicated by the rays1071-1073 which typically has a uniform NA across the backlightilluminates the back surface of the microdisplay and after propagationthrough the variable NA component is converted into output imagemodulated light indicated by the divergent ray pairs 1072-1074 with NAangles varying along the X axis.

In some embodiments the principles of the invention may be applied to anemissive display. Examples of emissive displays for use with theinvention include ones based on LED arrays and light emitting polymersarrays. In the embodiment of FIG. 17 the IIN 265 comprises an emissivemicrodisplay 266 and a spatially-varying NA component 267. Light fromthe microdisplay indicated by the rays 1077-1079 which typically has auniform NA across the emitting surface of the display illuminates thespatially-varying NA component and is converted into output imagemodulated light indicated by the divergent ray pairs 1080-1082 with NAangles varying along the X axis.

The invention does not assume any particular design for the microdisplayoptics. In some embodiments the microdisplay optics comprises apolarizing beam splitter cube. In some embodiments the microdisplayoptics comprises an inclined plate to which a beam splitter coating hasbeen applied. In some embodiments the microdisplay optics comprises awaveguide device comprising a SBG which acts as a polarization selectivebeam splitter based on some of the embodiments of U.S. patentapplication Ser. No. 13/869,866 entitled HOLOGRAPHIC WIDE ANGLE DISPLAY,and U.S. patent application Ser. No. 13/844,456 entitled TRANSPARENTWAVEGUIDE DISPLAY. In some embodiments the microdisplay optics containsat least one of a refractive component and curved reflecting surfaces ora diffractive optical element for controlling the numerical aperture ofthe illumination light. In some embodiments the microdisplay opticscontains spectral filters for controlling the wavelength characteristicsof the illumination light. In some embodiments the microdisplay opticscontains apertures, masks, filter, and coatings for controlling straylight. In some embodiments the microdisplay optics incorporate birdbathoptics.

We next describe exemplary embodiments of the spatially-varying NAcomponent. In some embodiments the spatially-varying NA component has auniformly varying NA characteristic. In some embodiments are provided ina stepwise fashion. It should be various exemplary embodiments of thespatially-varying NA component are illustrative only and, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, orientations,etc.). For example, the position of elements may be reversed orotherwise varied and the nature or number of discrete elements orpositions may be altered or varied.

In some embodiments such as the one illustrated in illustrated in FIG.18A a spatially-varying NA component 270 comprises a wedge 271. In someembodiments such as the one illustrated in FIG. 18B a spatially-varyingNA component 272 comprises a wedge having a curved surface 273. In someembodiments such as the one illustrated in FIG. 18C a spatially-varyingNA component 274 comprises an array of prismatic elements havingdiffering prism angles such as the elements 275,276. In some embodimentssuch as the one illustrated in FIG. 18D a spatially-varying NA component277 comprises an array of lenses having differing apertures and opticalpowers such as the lens elements indicated by 278,279.

In some embodiments such as the one illustrated in FIG. 19A aspatially-varying NA component 280 comprises an array of scatterelements such as the elements 281A,281B providing differing scatteredray angular distributions such as the ones indicated by 282A,282Brespectively. In some embodiments the scattering properties may beprovided by surface textures applied to a substrate. In some embodimentthe scattering properties may be provided by the bulk properties of thesubstrate. In some embodiments the substrate may contain particlessuspended in a matrix of refractive index differing from that of theparticle material. In some embodiments the substrate may be a PDLCmaterial. In some embodiments such as the one illustrated in FIG. 19B aspatially-varying NA component 283 comprises a substrate 284 having acontinuously varying scattering characteristics as indicated by thescattered ray angle distributions 285A,285B. The scattering propertiesmay be provided by surface or bulk medium characteristics.

In some embodiments such as the one illustrated in FIG. 19C aspatially-varying NA component 286 comprises a birefringent substrate287 having a spatially varying birefringence as represented by theuniaxial crystal index functions 288A, 288B. In some embodiments thesubstrate provides a continuous variation of birefringence. In someembodiments the substrates comprises discrete elements each have aunique birefringence. In some embodiments a spatially-varying NAcomponent is a scattering substrate with birefringent properties. Insome embodiments a spatially-varying NA component is based on any of theembodiments of FIGS. 18A-18D implements using a birefringent substrate.In some embodiments the NA variation across the field is performed usinga birefringent layer having comprising a thin substrate coated with aReactive Mesogen material. Reactive Mesogens are polymerizable liquidcrystals comprising liquid crystalline monomers containing, for example,reactive acrylate end groups, which polymerize with one another in thepresence of photo-initiators and directional UV light to form a rigidnetwork. The mutual polymerization of the ends of the liquid crystalmolecules freezes their orientation into a three dimensional pattern.Exemplary Reactive Mesogen materials are manufactured by Merck KgaA(Germany).

In some embodiments such as the one illustrated in FIG. 19D aspatially-varying NA component 286 comprises an array of diffractiveelements each characterized by a unique K-vector and diffractionefficiency angular bandwidth. For example element 289A at one end of thecomponent has k-vector K₁ and bandwidth Δθ₁ configured to provide a highNA while element 289B at the other end has k-vector K₂ and bandwidth Δθ₂configured to provide a low NA. In some embodiments the gratingcharacteristics vary continuously across the substrate. In someembodiments the gratings are Bragg holograms recorded in HPDLCmaterials. In some embodiments the gratings are surface relief gratings.In some embodiments the gratings are computer generated diffractivestructures such as computer generated holograms (CGHs).

In some embodiments the IIN design addresses the NA variation problem,at least in part, by tilting the stop plane such that its normal vectoris aligned parallel to the highest horizontal field angle, (rather thanparallel to the optical axis). As illustrated in FIG. 20 the IIN 287 isconfigured to provide an output field of view of half angle θ defined bythe limiting rays 1086, 1086B disposed symmetrical about the opticalaxis 1087. The stop plane 1088 is normal to the limiting ray 1086B. Itis assumed that the waveguide input grating, which is not illustrated,couples the horizontal field of view into the waveguide (not shown).

As discussed above, in some embodiments such as the one illustrated inFIG. 10 the waveguide display is coupled to the IIN by anopto-mechanical interface that allows the waveguide to be easilyretracted from the IIN assembly. FIG. 21A shows a removable near eyedisplay 290 comprising a near eye waveguide component and an IIN. Thewaveguide component includes an opto-mechanical interface for couplingto the IIN. The waveguide is shown retracted from the IIN assembly. FIG.21B shows a second 3D view of the HMD 296 with the waveguide componentretracted. FIG. 21C shows a 3D view of HMD 297 with the waveguidecomponent and IIN connected and ready for use.

FIG. 22 show schematic front views of two waveguide grating layouts thatmay be provided by the invention. In the embodiment of FIG. 22A thewaveguide 300 comprises a shaped waveguide comprising in a single layerindicted by 1086 an input grating 302, a fold grating 303 and an outputgrating 304. The K-vectors of the three gratings that is the normalvector to the fringes shown inside each grating are indicated by the1083-1084. Not that in each case the K-vector is projected in the planeof the drawings. The overall dimensions of the waveguide are 60 mm.horizontal by 47 mm. vertical. In the embodiment of FIG. 22B thewaveguide 310 comprises a shaped waveguide comprising in a single layerindicted by 1090 an input grating 313, a fold grating 314 and an outputgrating 315. The K-vectors of the three gratings that is the normalvector to the fringes shown inside each grating are indicated by the1087-1089. In each case the K-vector is projected in the plane of thedrawings. The overall dimensions of the waveguide are 75 mm. horizontalby 60 mm. vertical. FIG. 23 shows a further general waveguide gratinglayout that may be provided by the invention. The waveguide 320comprises a rectangular waveguide comprising in a single layer an inputgrating 322, a fold grating 323 and an output grating 324. The K-vectorsof the three gratings that is the normal vector to the fringes showninside each grating are indicated by the 1091-1093. In each case theK-vector is projected in the plane of the drawings. The fold grating inthis case has Bragg fringes aligned at 45 degrees in the plane of thegrating.

FIG. 24 is a 3D illustration of a near display comprising an IIN andwaveguide component in one embodiment. |the display 330 comprises an IIN331, waveguide 332 containing in a single layer an input grating 33 afold grating 334 and an output 335. The waveguide path from entrancepupil 2000 through the input grating, fold grating and output gratingand up to the eye box 2005 is represented by the rays 2001-2004.

FIG. 25 is a 3D illustration of one embodiment in which there isprovided a motorcycle HMD 340 using a near eye waveguide 343 with anopto-mechanical interface 344 for coupling to the IIN 345 which formspart of the helmet. The apparatus is similar to that illustrated in FIG.21 . FIG. 25A shows a first operational state 341 in which the waveguidecomponent is fully retracted from the IIN assembly. FIG. 25B shows thedisplay in its operational state 342 with the waveguide componentconnected to the IIN.

In some embodiments a dual expansion waveguide display according to theprinciples of the invention may be integrated within a window, forexample, a windscreen-integrated HUD for road vehicle applications. Insome embodiments a window-integrated display may be based on theembodiments and teachings disclosed in U.S. Provisional PatentApplication No. 62/125,064 entitled OPTICAL WAVEGUIDE DISPLAYS FORINTEGRATION IN WINDOWS and U.S. Provisional Patent Application No.62/125,066 entitled OPTICAL WAVEGUIDE DISPLAYS FOR INTEGRATION INWINDOWS. In some embodiments a dual expansion waveguide display mayinclude gradient index (GRIN) wave-guiding components for relaying imagecontent between the IIN and the waveguide. Exemplary embodiments aredisclosed in U.S. Provisional Patent Application No. 62/123,282 entitledNEAR EYE DISPLAY USING GRADIENT INDEX OPTICS and U.S. Provisional PatentApplication No. 62/124,550 entitled WAVEGUIDE DISPLAY USING GRADIENTINDEX OPTICS. In some embodiments a dual expansion waveguide display mayincorporate a light pipe for providing beam expansion in one directionbased on the embodiments disclosed in U.S. Provisional PatentApplication No. 62/177,494 entitled WAVEGUIDE DEVICE INCORPORATING ALIGHT PIPE. In some embodiments the input image source in the IIN may bea laser scanner as disclosed in U.S. Pat. No. 9,075,184 entitled COMPACTEDGE ILLUMINATED DIFFRACTIVE DISPLAY. The embodiments of the inventionmay be used in wide range of displays including HMDs for AR and VR,helmet mounted displays, projection displays, heads up displays (HUDs),Heads Down Displays, (HDDs), autostereoscopic displays and other 3Ddisplays.

Some of the embodiments and teachings of this disclosure may be appliedin waveguide sensors such as, for example, eye trackers, fingerprintscanners and LIDAR systems.

It should be emphasized that the drawings are exemplary and that thedimensions have been exaggerated. For example thicknesses of the SBGlayers have been greatly exaggerated. Optical devices based on any ofthe above-described embodiments may be implemented using plasticsubstrates using the materials and processes disclosed in PCTApplication No.: PCT/GB2012/000680, entitled IMPROVEMENTS TO HOLOGRAPHICPOLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES. In someembodiments the dual expansion waveguide display may be curved.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (for example, variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions and arrangement of the exemplaryembodiments without departing from the scope of the present disclosure.

What is claimed is:
 1. An optical display, comprising: a first waveguidehaving a first surface and a second surface; a first input coupler; afirst fold grating; a first output grating; a polarization component;and an input image node (IIN) including a liquid crystal-based displaypanel, wherein said first input coupler is configured to receivecollimated first wavelength image modulated light and to cause saidfirst wavelength image modulated light to travel within the firstwaveguide via total internal reflection between said first surface andsaid second surface to said first fold grating, wherein said first foldgrating is configured to provide pupil expansion in a first directionand to direct said first wavelength image modulated light to the outputgrating via total internal reflection between the first surface and thesecond surface, wherein said first output grating is configured toprovide pupil expansion in a second direction different than said firstdirection and to cause said first wavelength image modulated light toexit said first waveguide from said first surface or said secondsurface, wherein at least one of said first input coupler, said firstfold grating, or said first output grating is a liquid crystal-basedgrating having a preferred polarization sensitivity, wherein saidpolarization component rotates the polarization of the first wavelengthlight into a polarization state that provides efficient coupling withsaid liquid crystal-based grating, wherein at least one of said firstinput coupler, said first fold grating or said first output grating is arolled k-vector grating, and wherein said first wavelength imagemodulated light undergoes a dual interaction with said first foldgrating.
 2. The optical display of claim 1, wherein said IIN comprises alight source and a microdisplay for displaying image pixels andcollimation optics, and wherein said IIN projects the image displayed onsaid microdisplay such that each image pixel is converted into a uniqueangular direction within said first waveguide.
 3. The optical display ofclaim 2, wherein said IIN further comprises a spatially-varyingnumerical aperture component for providing a numerical aperturevariation along a direction corresponding to a field of view coordinatediffracted by said first input coupler.
 4. The optical display of claim3, wherein said spatially-varying numerical aperture component has atleast one of diffractive, birefringent, refracting or scatteringcharacteristics.
 5. The optical display of claim 3, wherein said fieldof view coordinate is a horizontal field of view of the optical display.6. The optical display of claim 3, wherein a spatially varying-numericalaperture is provided by tilting a stop plane such that its normal vectoris aligned parallel to a highest display field angle in the stop planecontaining the field of view coordinate diffracted by said first inputcoupler.
 7. The optical display of claim 1, wherein at least one of saidfirst fold grating or said first output grating is switchable between adiffracting and non-diffracting state.
 8. The optical display of claim1, further comprising a second waveguide comprising a first surface anda second surface, a second input coupler, a second fold grating, and asecond output grating, wherein said second input coupler of said secondwaveguide is configured to receive collimated second wavelength imagemodulated light from said IIN.
 9. The optical display of claim 8,further comprising a dichroic filter disposed between said first inputcoupler and said second input coupler.
 10. The optical display of claim1, wherein said first input coupler is one of a grating or a prism. 11.The optical display of claim 1, wherein said first direction isorthogonal to said second direction.
 12. The optical display of claim 1,wherein said first direction is horizontal and said second direction isvertical.
 13. The optical display of claim 1, further comprising an eyetracker.
 14. The optical display of claim 1, further comprising adynamic focus lens disposed in said IIN.
 15. The optical display ofclaim 1, further comprising a dynamic focus lens disposed in proximityto the first or second surface of said first waveguide.
 16. The opticaldisplay of claim 1, wherein said first waveguide further comprises afirst optical interface said IIN further comprises a second opticalinterface wherein said first and second optical interface can bedecoupled by one of a mechanical mechanism or a magnetic mechanism. 17.The optical display of claim 16, wherein said first waveguide isdisposable.
 18. The optical display of claim 1, wherein said firstsurface and said second surface are planar surfaces.
 19. The opticaldisplay of claim 1, wherein said first surface and said second surfaceare curved.
 20. The optical display of claim 1, wherein said IINcomprises a laser scanner.
 21. The optical display of claim 1, whereinsaid optical display provides one of a HMD, a HUD, an eye-slaveddisplay, a dynamic focus display or a light field display.
 22. Theoptical display of claim 1, wherein at least one of said first inputcoupler, said first fold grating and said first output gratingmultiplexes at least one of color or angle.
 23. The optical display ofclaim 1, further comprising a beam homogenizer.
 24. The optical displayof claim 1, wherein said optical display includes at least one opticaltraversing a gradient index image transfer waveguide.
 25. The opticaldisplay of claim 1, wherein said polarization component is a quarterwave plate.
 26. The optical display of claim 1, wherein saidpolarization component is a substrate overlaying said liquidcrystal-based display panel and has a spatially varying birefringence.27. The optical display of claim 1, wherein said liquid crystal-baseddisplay panel, operates in reflection.
 28. The optical display of claim1, wherein said liquid crystal-based grating has maximum diffractionefficiency for P-polarized light.